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The Accuracy of DNA Results

Millions of people have taken DNA tests to determine their ancestry, but one Massachusetts man is questioning the accuracy after getting conflicting results from two genetic companies.

(Published Tuesday, March 12, 2019)

What to Know

Paul Genest ordered DNA kits from Ancestry and 23andMe.

Both test results found that Genest is more than 60 percent Irish and British, but the rest of the results varied.

NBC10 Boston Responds found that genetics companies use different algorithms and reference population data.

Millions of people have done it and you may be one of them – sent off a saliva sample to figure out your DNA ancestry. But one Massachusetts man is questioning how accurate these tests really are after getting different results from two genetics companies.

Paul Genest, of Swampscott, knows a lot about his family history, and he considers himself to be predominately of French descent.

“From chit chat within the family, and given the fact that everyone spoke French, we were pretty certain we were French,” said Genest.

But he got a surprise when the results came in after he ordered DNA kits from Ancestry and 23andMe.

“If you look at the difference between the two, there are discrepancies in every major group, and it turns out I’m not as French as I thought I was,” said Genest.

Both test results found that Genest is more than 60 percent Irish and British, but the rest of the results varied.

“There were things that matched and things that didn’t match,” said Genest. “The biggest thing was that Ancestry left out 11 percent and between 23andMe and Ancestry there was well over 20 percent disagreement in their information. So which one of them do you believe?”

NBC10 Boston Responds turned to Dr. Lindsay Farrer, the Chief of Biomedical Genetics at Boston University School of Medicine to get some answers.

“Some of it is accurate. Some of it is less accurate,” said Farrer.

He said the DNA tests are very good at determining your close relatives who have also submitted samples, but when it comes to where you come from, Farrer says the results are dependent on the reference sample that the company is using to determine genetic make-up.

“There are some populations that are unique genetically, so if they tell you have Icelandic heritage or Finnish heritage, that’s probably accurate,” said Farrer. “Once you start getting into populations that are currently defined geographically by national boundaries, such as in many places in Europe, that info can vary in its accuracy.”

Farrer adds, even if the two companies were using the same reference sample, there may still be discrepancies.

“The algorithms they apply to correlate the signatures derived from one population may be different from the way another company does it. One isn’t necessarily wrong or less reliable than the other, but just shows the limits of the precision in some of the estimates,” said Farrer.

NBC10 Boston Responds reached out to 23andMe and Ancestry about Genest’s tests.

23andMe told NBC10 Boston, “Each testing company uses a different algorithm and different reference populations to identify where in the world your DNA is from. 23andMe is extremely confident in our results, and are consistently ranked the most accurate DNA testing service by industry trade groups.”

So you may want to think about your DNA test results as different components of your background, rather than fixating on the exact percentages. As for Genest, if someone asks him where his ancestors come from he’s going to say France!

If you did a DNA test in the past and recently received a revised report, it’s because the companies regularly update their algorithms and reference population data in order to achieve more precise results.